It is well known that the complete failure of steel cord-reinforced conveyor belts as used on conveyor belt structures in various mining and industrial applications can have catastrophic results. As such, condition monitoring of these conveyor belts has become common practice, the objective being to identify damage to conveyor belts and thus to effectively maintain conveyor belts.
A typical steel cord-reinforced conveyor belt as herein envisaged is made up of elongated conveyor belt sections, typically in the order of 300 m in length.
Each section comprises a central layer of multi-stranded steel cords sandwiched in a substantially equally-spaced, parallel configuration between two rubber layers, the sections being connected by means of splices. A splice between two sections is formed by overlapping the ends of the two sections by one to five meters and vulcanizing the sections together. When the sections are so connected, the cords of the sections in the overlapping region are arranged in a pattern in which alternating cords of the sections lie in a parallel adjacent relationship.
It is known to monitor conveyor belts for cord breaks by magnetizing the cords using a permanent magnet array and then detecting fringing magnetic fields resulting from breaks. The condition of splices may also be monitored in this manner.
However, this technique has a serious deficiency. There is only a detectable magnetic field just above the cord break or just above the cord end. Thus the magnetic image above intact cords is blank—i.e. they are magnetically invisible.
If for example for a new belt, here are many unbroken long cords, then after magnetizing, the magnetic image will be blank except for a single dip at one end (the south pole) of these cords and a peak at the other end (north pole). There is in fact a very small dipole magnetic field that exists between these very separated poles. However, since the cords of a new belt segments are typically 2-30 Om apart, the resulting magnetic field is very small and difficult to detect.
With a new belt it is desirable to know the number of cords thereof and their spacing, which is not possible to do with such existing technology. Also, in some applications cords are placed across the belt at 45° in order to detect rips, since if a longitudinal rip occurs, this will cut these diagonal cords and produce additional north/south pole pairs where none were previously present. However again, intact transverse cords are invisible with present magnetic field detection technology. It is again desirable to be able to detect the presence of the diagonal cords and hence confirm that the rip detection functionality was intact.
It is thus an object of this invention to provide a method of and an apparatus for the above purpose and in respect of which the above inadequacies are at least ameliorated.